A cryopump generally produces a high vacuum by adsorbing a gas molecule to an adsorption panel installed on a coldhead of a refrigerator. It is required in the cryopump that a cooling temperature for the adsorption panel is held in a designated range while the adsorption panel adsorbs a gas molecule.
For example, a cryopump exclusive for water requires the cooling temperature for the adsorption panel 3 (FIG. 1) to be held in the range of about 110K. FIG. 1 is a general view of the cryopump exclusive for water. In FIG. 1, there are shown a refrigerator 1 which may be a GM (Gifford-McMahon) refrigerator, a coldhead 2, an adsorption panel 3 installed on the coldhead 2, a vacuum space 4 in use of the cryopump and a fixture flange 5.
At present, a GM refrigerator is mainly employed to cool the cryopump, wherein helium gas (single gas) is used as an operating gas. During a normal operation the temperature of the adsorption panel 3 decreases to not greater than 110K (in some cases the temperature decreases to as low as 30 to 40K), and thus deviating from an original purpose to eliminate only water by freezing, other gas components may be frozen. To obviate such a problem, the cryopump exclusive for water is provided with a heater and a thermometer (both are not shown in the figure) on the coldhead 2 for holding a temperature. The adsorption panel 3 can hold its temperature by controlling the temperature of the heater.
However, the conventional cryopump has a heater wiring led out of the vacuum space 4 into the atmosphere, requiring a complicated seal with a high risk of leakage. Further, a temperature controller is necessary in order to follow heat load changes (for example, when water is excessively attached to the adsorption panel 3 or when the vacuum degree is lowered, the temperature of the adsorption panel 3 is increased, necessitating control the temperature control of the heater). Therefore, a complicated mechanism is required, resulting in a cost increase.
In Japanese Patent Publication TOKKAIHEI 6-73542, a cryopump is disclosed which includes, as temperature control means for the adsorption panel 3, a heat exchanger, a connector connecting the heat exchanger to the adsorption panel 3, transport means for transporting a cooling medium such as helium gas to the heat exchanger, means for regulating a flow rate of the cooling medium and the like. However, the above-disclosed cyropump also requires a complicated mechanism with a cost increase.
In view of the foregoing, it is an object of the present invention to provide a pulse tube refrigerator which can hold a cooling temperature without the use of a heater and the like and a cryopump using the pulse tube refrigerator.